Model railway installations generally are arranged to operate e.g. from a nominally 15 volt direct current supply generally derived from the mains alternating current supply by transformation and rectification. The model locomotives incorporate miniature d.c. motors arranged to be powered from the track, which is connected to the 15 volt supply, through one or more sliding contactors carried by the locomotive and/or through the contact of the locomotive wheels with the track. Any dust, grease, metal oxide and the like on the track can interrupt the continuous supply of driving power to the locomotive causing it to stop or at least to falter in its progress. Once the locomotive has stopped owing to disruption of its electrical connection with the track, it generally cannot be restarted merely by operation of the speed/go/stop controller of the installation and needs to be moved manually to another, clean part of the track.